1. Field of the Invention
The invention relates to a dual panel display, and more particularly, to a dual panel display with a structured that can improve the mura or uneven-brightness problems.
2. Description of the Prior Art
The liquid crystal display (LCD) is a thin and save electricity flat display. It uses a backlight source to produce light, and uses the different liquid crystal revolving angles and the polarized light layer beside the liquid crystal to control the transmittance for displaying images. The LCD has advantages of stable appearance and no twinkle, and therefore LCDs have been widely applied to many devices, such as mobile phone, PDA, notebook, digital camera or other portable products. Owing to new products continuously entering the market, the technology of the LCD also keeps on improving. The latest fashion is to dispose dual panel displays on various products.
Fox example, modern design of mobile phones is to dispose two displays on two sides of the mobile phone, wherein one of the two displays is a main display panel and the other one is a sub-display panel. The sub-display panel display images on the outer side of the housing of the mobile phone for displaying simple characters or image signals such that the user can read information from the sub-display without answering phone calls. On the other hand, the main display panel is usually disposed on the inner side of the housing of the mobile phone for displaying complicated information or image signals.
With reference to FIGS. 1-3, FIGS. 1-2 are a front and a back schematic diagrams of a dual panel display 10 according to the prior art respectively, and FIG. 3 is a sectional view of the dual panel display 10 shown in FIG. 1. As shown in FIG. 1, the dual panel display 10 includes a housing 14 and a main display panel 16, wherein the region encompassed by the dotted line is a display region 34 of the main display panel 16. FIG. 2 illustrates that the housing 14 has a fixing frame 14c for positioning a sub-display panel 18 with a smaller size than the main display panel 16, wherein the region encompassed by the dotted line is a display region 36 of the sub-display panel 18. The relative position of other elements of the dual panel display 10 is illustrated in FIG. 3. The housing 14 includes a fixing plane 14a for containing the main display panel 16 and the backlight module 12. The backlight module 12 typically comprises a light source 20, a light guide plate 22, and further comprises a diffuser film 30, two prism films 28, 26, and a protect diffuser film 24 positioned on the light guide plate 22 in order. On the other side of the fixing plane 14a, the sub-display panel 18 and some optical films of the sub-display panel 18 are positioned near the fixing plane 14a while only a diffuser film 32 is illustrated in FIG. 3. In addition, the fixing plane 14a further comprises an opening 14b with a size approximately equal to the size of the sub-display panel 18.
The theory of the prior art dual panel display 10 is described as below: The light source 20 produces light so that light propagates into the light guide plate 22 and diffuses in the whole light guide plate 22. Then, a part of light propagates through the first light-exit surface 40 of the light guide plate 22 and passes through the diffuser film 30, the prism films 28, 26, and the diffuser film 24 so as to enter the main display panel 16; and the other part of light propagates through the second light-exit surface 42 of the light guide plate 22 to the fixing plane 14a of the housing 14 and is reflected back to the light guide plate 22 to further provide light source to the main display panel 16. However, when light from the second light-exit surface 42 propagates to the opening 14b, it will pass through the fixing plane 14a and enter the diffuser film 32 to provide light source to the sub-display panel 18. Since partial light passes through the opening 14b to the sub-display panel 18, a relatively dark region occurs in the display region 34 of the main display panel 16, which corresponds to the area of the sub-display panel 18 and is called a window problem or a mura problem of the main display panel 16.
For solving the mura problem, the conventional method pays attention to researching and designing the pattern of the light guide plate 22. For example, a special pattern may be designed for the portion of the light guide plate 22 corresponding to the opening 14b in order to uniform the brightness or increase brightness of the region occurring the window problem. However, the method of designing the pattern of the light guide plate 22 is complicated and costs much time, and it is uneasy to achieve a satisfying performance through designing the pattern of the light guide plate 22. Besides, according to the prior-art method, the pattern of the light guide plate 22 has to be re-designed when the position of the sub-display panel 18 is changed in different application.
In addition, the fixing plane 14a has a thickness Th, so the gap between the light guide plate 22 and the diffuser film 32 must be larger than the thickness Th, which causes an optical defect at the position of the opening 14b, resulted in a more serious window problem in the main display panel 16 corresponding to the edge of the opening 14b. 
To conclude, how to improve the mura problem or window problem of the main display panel in a dual panel display caused by providing light to the sub-display panel through a simple and effective method is still an important issue for the manufacturers.